Outcome vs. Event: What’s the Difference?


Two terms that students often confuse in statistics are outcome and event.

Here’s the subtle difference between the two terms:

Outcome: The result of a random experiment.

  • For example, there are six potential outcomes when rolling a die: 1, 2, 3, 4, 5, or 6.

Event: A set of outcomes that has a probability assigned to it.

  • For example, one possible “event” could be rolling an even number. The probability that this event occurs is 1/2.

The following examples show more scenarios that illustrate the difference between outcomes and events.

Example 1: Deck of Cards

Suppose we randomly draw a card from a standard deck of 52 cards.

The four possible outcomes for the suit of the card include:

  • Heart
  • Spade
  • Diamond
  • Club

One of these four outcomes must occur.

However, there are many different events that we may be interested in assigning a probability to. For example:

Event 1: Draw a Heart

  • The probability that this event occurs is 13/52 or 1/4.

Event 2: Draw a Heart or a Spade

  • The probability that this event occurs is 26/52 or 1/2.

Event 3: Draw a card that is not a Heart

  • The probability that this event occurs is 39/52 or 3/4.

There are many more events that we could come up with and assign a probability to, but these are just three simple ones.

Example 2: Pulling Marbles from a Bag

Suppose a bag has 3 red marbles, 5 green marbles, and 2 blue marbles.

If we close our eyes and randomly select one marble from the bag, the three possible outcomes for the color of the marble include:

  • Red
  • Green
  • Blue

One of these four outcomes must occur.

However, there are many different events that we may be interested in assigning a probability to. For example:

Event 1: Draw a Blue Marble

  • The probability that this event occurs is 2/10 or 1/5.

Event 2: Draw a Blue or Green Marble

  • The probability that this event occurs is 7/10.

Event 3: Draw a Marble that is not Blue

  • The probability that this event occurs is 8/10 or 4/5.

These are three events that we can easily calculate probabilities for.

Additional Resources

How to Find the Probability of “At Least One” Success
How to Find the Probability of A or B
How to Find the Probability of A and B

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